Most existing magnetoresistive (MR) sensors, including particularly sensors for bubble memories and magnetic recording, are biased at a constant bias current by preamplifiers which detect the signal voltage developed at the sensor terminals. Since stripe height is inversely proportional to sensor resistance, and varies from sensor to sensor owing to production variations and varies over the life of the sensor in contact recording applications owing to wear, it is desirable to detect signals produced by the sensor which are independent of stripe height. Thus, as shown in the related application, it is desirable to detect and amplify a voltage representing .DELTA.R.sub.h /R.sub.h, where .DELTA.R.sub.h is the change in MR sensor resistance, R.sub.h, arising from the magnetic input signal from the media being read.